A reader (Franto) asks "Sorry to butt in with this question for you! I had a recent sleep study that showed I am getting v little REM sleep because I start getting hypopneic as soon as I enter into REM and have an arousal. Overall there was little obstruction and no apnea (lowest O2 sat was 91%). The problem was entirely REM specific, and I had good deep sleep. My total REM percentage was only 6.5%. There apparently were several aborted REM episodes. The reason I had the study done was that I have been having unrefreshing sleep and working memory issues for a few years now! My sleep physician wants me to do CPAP study to see if it helps improve my REM. My Q to you is if you see cases like mine at all, since I havent read about such a selective REM condition on the web or Pubmed. I know about UARS but that too involves both REM and NREM. Would CPAP help in such a situation?"
Some people have OSA primarily during REM sleep. I found the following in Sleep Medicine Pearls, by Richard B. Berry, MD (2nd edition, page 118):
In patients with excessive daytime sleepiness and significant, REM-specific sleep apnea, treatment is indicated. Other possible causes of daytime sleepiness should be excluded.
The reason for the higher AHI during REM sleep are commplex. REM sleep is not homogenous, and episodes of decreased upper airway muscle activity or ventilatory drive may be the cause of hypopneas or apneas during REM sleep.
In my experience, in many people, OSA is worse during REM sleep. It is unusual for sleep apnea to occur exclusively during REM, but it is possible. I think your sleep physician's advice is reasonable and CPAP is worth a try.